This program addresses regulation of gene expression in the developing immune system. The goal is to elucidate the mechanism of transcriptional regulation of major histocompatibility complex (MHC) class I genes, which play an important role in development and function of the immune system. Our major efforts have been the isolation and characterization of cDNA clones encoding proteins that bind to the conserved cis regulatory elements involved in controlling MHC class I transcription. So far, we have isolated five cDNA clones, three of which have been studied in detail. H-2RIIBP: this is a Zn finger protein that belongs to the nuclear hormone receptor superfamily, and binds to the enhancer region II of the MHC class I gene, and other cis elements, such as the estrogen and thyroid hormone response elements. We show that H2RIIBP trans-activates the MHC class I-CAT reporter gene when transfected into embryonal carcinoma cells. The trans-activation is dependent on the presence of retinoic acid or Vitamin A. RIBP (CRYBP): this protein has two domains of a C2H2 Zn finger. It binds to the enhancer region I, and cis elements of many other genes including the NFkB site in the immunoglobulin, beta-2 microglobulin, and lens crystallin alpha gene. Monoclonal and polyclonal antibodies raised against RIBP recombinant proteins react with proteins of M.W., smaller than that expected of the cDNA, suggesting that RIBP (CRYBP) undergoes processing. ICSBP: this factor binds to the interferon consensus sequence (ICS), a cis element responsible for interferon (IFN) mediated transcriptional induction of MHC class I gene. The ICSBP belongs to the IRF family and binds to the IFN response elements present in the IFN genes and other genes regulated by IFN. ICSBP is expressed predominantly in lymphoid tissues, and inducible by IFN-gamma, suggesting that it is a multi-functional mediator affecting various aspects of immune regulation. These studies highlight the existence of large families of regulatory genes which have distinct DNA binding domains and are conserved throughout the animal kingdom. Sequencing and initial characterization are still under way for two additional cDNA clones encoding proteins that bind to the negative regulatory element and the enhancer region Ill of the MHC class I gene. We have also begun analyzing DNA-protein binding in the MHC class I genes in vivo by using the PCR mediated in vivo DNA foot printing procedure.